On Electron-Nuclei Colliders A.Skrinsky (for ECooling & Colliders INP Teams) JLab 15-17/3/2004

Transcription

1 On Electron-Nuclei Colliders A.Skrinsky (for ECooling & Colliders INP Teams) JLab 15-17/3/2004

2 What for we need to use electron-nuclei collider approach? * Obviously: when we want to reach the effective energy higher than in electron accelerator target case (there is no very high energy electron accelerators ). SLAC & HERA-e the only (and successful) examples! * When we need to study rare nuclei (secondary and/or unstable?!). * Less obvious when we need to study bare nuclei (no background events with target electrons). 2

3 *Even less obvious - when we want to study collisions of longitudinally polarized electrons with longitudinally polarized nuclei with high degree of polarization and high luminosity ( no unpolarized nuclei or, in some layouts, no unpolarized electrons). * When we need the combination of extreme luminosity and high monochromaticity, small angular spread and small interaction spot (no energy losses and scattering of electrons external or internal) *Somewhat similar csae: not to disturb reaction products (mostly hadron interacting remnants) do not spoil purity and accuracy of the experiments. * Special case: interest to compare electron-nuclei processes with positron-(same) nuclei ones (e.g., of two-photon type) especially when we need polarized positrons)

4 Now it became a common sense: to reach high luminosity and good experimental quality for different types of experiments it is wise to apply Electron Cooling. Reasons to apply Electron Cooling (continuous or at some stages; maybe, in combination with Stochastic Cooling to rise effective acceptance): * storing of secondary stable and long enough living hadrons, nuclei and ions; * achieving of very low temperature of stored particles; * suppression of beam blow-up due to diffusive effects of different nature (multiple scattering by internal targets, external noise, multiple intra-beam scattering, beam-beam effects, ). * suppression of injection errors to prevent emittances growth. 4

5 Reqirements for electron cooling beam (still not very familiar): * to receive all the advantages of electron beam magnetization, the longitudinal guiding field in the cooling section should unidirectional within angular spread better than ion beam emittance angular spread. * not to excite additional oscillations in ion beam, the angle(s) between guiding field and the ion closed orbit should be also smaller than equilibrium angles in ion beam. * To prevent radiative recombination losses for heavy highly charged ions, keeping fast damping for large amplitude ions, there are 2 options: 1. to make Larmor velocities high enough (damping rate diminish logarithmically, only). 2. to arrange hollow electron cooling beam with the same full current, but with much lower density in the core 5 part of ion beam cross-section.

6 Hollow beams are useful to prvent overcooling (e..g., pbars). Another option for prevention to use monochromatic instability. 6

7 Variation of electron beam profile for optimization cooling The electron beam distribution for different voltage on the control electrode - 0, 100, 200, 350, 400, 600 V. The measuring was made with using tungsten wire by scanning across the electron beam. Beam diameter 3 cm. 7

8 Many crucial aspects of achieving high luminosity and, simultaniously, high quality of the experiments (especially, under continuous Electron Cooling were presented in my talks (as our Team representative) at Workshops at Uppsala (...), Indiana ( ) and Brookhaven ( ) (and references in that publications), and in many talks of my colleagues (especially, V.V.Parkhomchuk, Yu.M.Shatunov and I.A.Koop) and our collaborators. 8

9 Now, I intend to present some examples of projects we participate, and most important steps, related to the development of Electron Cooling for the kind of applications under discussion at the Workshop. Projects: GSI Lanzhou Brookhaven (Bates,.) CERN - LEIR Improvements hollow beams electrostatic bending High Voltage + contintinuous solenoids : List of recent design and constructions 9

10 ECoolers - storage rings. 10

11 ELECTRON COOLING NOVOSIBIRSK (Start of ECooling activity -1965) Proton Storage Ring NAP-M (experimental success 1974) (the view from injector side) 11

12 Electron Cooler, installed at NAP-M 12

13 BINP made cooler at SIS-18 13

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15 Accumulation Bi ions at GSI ( May 1998) 0.3 points - measurements solid line - fit Bi(+67)209, Je = 400 ma, exp. factor = 3 ion current [ma] di injected current time [sec]

16 IMP (Lanzhou) - project CSRe SFC CSRm SSC 16

17 35 kv Electron Cooler 1. Variable profile electron beam for suppression of the heating and electron capture 2. Electrostatic bends (suppression of current losses, better vacuum mbar now) 3. Precise pancake design of cooling section. EC-35 17

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19 19 EC- Novosibirsk

20 EC- Lanzhou (in place!) 20

21 E e =300 KeV 1 - electron gun; 2- main gun solenoid ; 4 - electrostatic deflectors; 5 - toroidal solenoid; 6 - main solenoid; 7 - collector; 8 - collector 21 solenoid; 11 - main HV rectifier; 12 - collector cooling system. 1 m

22 Установка электронного охлаждения на 300 кв: 1 высоковольтный фидер, 2 магнитный концентратор коллектора, 3 коллектор, 4 ускорительная (замедляющая) трубка коллектора, 5 катушки магнитного поля коллектора, 6 поворотный участок с электростатическими поворотами, 7 катушки тороидального магнитного поля, 8 катушки магнитного поля секции охлаждения (прямолинейный участок магнитного поля), 9 бак высоковольтного генератора, 10 магнитопровод соленоида, 11 магнитопровод тороидального участка магнитного поля, 12 титановые сублимационные насосы, 13 катушки магнитного поля электронной пушки, 14 магнитопровод соленоида электронной пушки, 15 ускорительная трубка электронной пушки, 16 электронная пушка, 17 концентратор магнитного поля электронной пушки, 18 местоположение высоковольтного терминала, содержащего 22 цифровую и силовую электронику управления пушкой и коллектором, 19 ионный насос, 20 дипольные корректоры ионного пучка.

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25 Last picture at Novosibirsk 25

26 Lanzhou now assembly process. 26

27 LEIR: space for future ECooler. 27

28 2478 e Ions Future LEIR in Novosibirsk 28

29 ECoolers - for higher energies and Colliders. 29

30 Electron-Nuclei Collider Conceptual Project (for GSI)!? (incl. ECooling) Electron-Proton Electron-Uranium. s maxe nucleon = 30 GeV L e nucleon = cm 2 s 1

31 ENC (GSI) Electron-Uranium s max = 30 GeV - per e-nucleon L e nucleon = cm 2 s 1

32 HESR objectives Antiproton energy GeV Number of stored antiprotons up to Luminosity of antiproton-proton collisions up to cm -2 sec -1 Target thickness to atoms/cm 2 (H 2 jet or pellets) Momentum spread of antiprotons ~ 10-5 Length of straight sections 105 m 32

33 General view of the HESR 33

34 For HESR the optimal solution is 8 MeV 1 A electrostatic cooler 1. easy change e- energy(0.8 8 MeV) 2. DC electron beam 3. low amplitude of HV ripple 34

35 8 MeV e-cooler 35

36 Electrostatic machine side view 12 m 3 5 m 1 E Cyclotron 30m Cooler solenoid view from above 3 2 R= 4m Cyclotron Cooler solenoid 4 30m Very schematic view of the electron cooling device for HESR 36 (H - cyclotron - for charging the e-generator up to 8 MeV!) 8m 2

37 1 2 Layout of 8 MeV cooler for HESR high voltage tank; 2 electrostatic column; 3 cyclotron for charging of electrostatic column head; 4 cooling section (30 m length); 5 return trace, 6 magnetic flux iron yoke, 37 7 edges of cooling section. 4

38 Transverse cross-section of high voltage column De- Accelerating tube N3 510 Drive axis Accelerating tube N1 Solenoid Accelerating tube N2 Solenoid Electrostatic DC accelerator with 3 accelerating tubes for: acceleration of e- beam deceleration of return e- beam charge of HV terminal by H- ion beam from small cyclotron. 2.Solenoids along electron beams ar powered by motorgenerators along high voltage column (common drive-shaft) 38 (locally powered!).

39 Preliminary engineering parameters of the cooler Acceleration column Electron energy on the output MeV Length 8.0 m Average electrostatic intensity along accelerated column kv/cm Magnetic field 500 G Cathode diameter ( beam diameter) 2 cm Hight of high-voltage vessel 13.0 m Diameter of high-voltage vessel with SF 6 gas 6.0 m Bending section. Magnetic field 5 kg (E e = MeV) 2 kg (E e = MeV) Bending radius 400 cm Beam diameter 0.6 cm (5 kg) 1.0cm (2 kg) Cooling section. Magnetic field 5 kg (E e = MeV) 2 kg (E e = MeV 39

40 e A NESR based colliders General layout of e-a collider

41 Luminosity of e-fragment collider vs. total number of stored ions 41

42 General requirements for e-fragment collider based on NESR storage GSI Revolutions of ion and electron beams are synchronized (quantized): Energies: E Momentum transfer range: Typical fragment yields: -10 U i Fe 5, 6, 7, 8, 9 F = 740 MeV/u, E 500 MeV 20 q 400 MeV/c Stacking provides : (Depending on their lifetimes) 7 5 fragments/pulse isotopes Intense electron cooling!!! Provides stacking and suppress blow-up due to intrabeam scattering Low momentum spread and emittance control Significantly increase achievable beam-beam limit Electron beam energy spread: Electron beam angular divergence: Electron bunch intensity limitation: Bunch length: 10 cm i E e kev θ 1mrad e e 10 Nbe 510 σ = 42 s

43 General parameters of the e-fragment collider for the case of A=238, Z=92 and β i = Units Electron ring Ion ring Circumference m Energy GeV, GeV/u Revolution frequency MHz Betatron tunes, ν x, ν y 3.8, , 3.8 Compaction factor, α Bending radius m Number of bunches 8 40 Bunch to bunch spacing m Bunch population Beam currents ma Energy losses/turn kev Total radiated power kw 1.88 Damping time, τ ms Beam emittances, ε x, y µm mrad Beta functions at IP, β x, y cm 100, , 15 Beam size at IP, σ x, y µm 220, , 87 Beam divergence at IP, σ x, y mrad 0.22, , 0.58 Momentum spread, σ p/p Bunch length, σ s cm 4 15 Beam-beam parameters, ξ x, y 0.005, , Laslett tune shift, ν 0.1 Luminosity cm -2 s

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45 Closer look on the interaction region layout. Different versions with different magnet free space near IP. 45

46 A e cm Layout of the interaction region of the e-a collider. 46

47 Electron cooling and ea Collider for NESR (another layout) Cooling section Accelerating voltage kv Maximum electron current 2 A Electron beam diameter 25 mm Magnetic field strength 0.2 T Transverse electron temperature 0.2 ev Length of cooling section 4 m Field parallelity in cooling section, B trans /B long

48 Yet another layout of the electron ring. Version with ±2.0 m of a magnet free space near the IP. (maybe, for pbar-a collisions?) 48

49 Cooling for HESR r.m.s emittance (mm*mrad*pi) 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0,0 14 GeV Je=0 no cooling Je=0.1 A Je=1 A time (s) R.M.S. emittance vs. time with and without electron cooling 49

50 General view of the erhic Collider 50

51 Plus: RHIC based Electron - Nuclei Collider. RHIC Electron Cooling for Luminosity Enhancement Initial parameters for the electron cooling system for RHIC Parameter Symbol Value Units Electron beam energy E e 50 MeV Peak electron beam current J e 1 A Length of electron bunch L e 50 cm Fraction cooler at circumference η e Number of electron at bunch N e DC electron current Je DC =e*n e *f b 7.4 ma Beta function at cooling section β x 60 m Ion beam radius a e = (ε nt *β x /γβ) 0.08 cm Ion beam divergence at cooling sect. θ= (ε nt /(β x β γ )) rad Ions transverse velocity at the ion V i =γβ c θ cm/s beam s reference system Electron beam density at the ion beam s reference system n e 10 8 cm -3

52 Schematic layout of the cooling system (next to a RHIC interaction point) The hope: 10 times higher average luminosity for A-A, for ea and for lngitudinally polarized ep collisions. A e 52

53 Project of electron cooling for RHIC 50 MeV 1 A 53

54 400 1 x R θ R Figure Achromatic bend. 1 and 4 parallel edges magnets, 2 and 3 magnetic mirrors, 5 sextupole corrector. d l y 54

55 Electron cooling for e-p collider 1 main linac, 2 Chicane magnet system for bunching/debunching, 3 adaptor for to come in/out solenoid. 55

56 Schematic Layout of Electron Cooling for RHIC Photoinjector (laser photocathode RF gun) Superconducting energy-recovery linac e - Beam dump SC Solenoid 1T field A 56

57 The needs for electron cooling: Electron cooling in erhic 1. E-cooling for gold beam at storage phase to control MIBS and reduce emittance. 2. E-cooling for protons at injection - to reduce transverse beam emittance. 3. Cooling the longitudinal emittance bunch shortening to match with a low β* in the IP. Cooling of proton bunch (N p = , 27 GeV) Emittance growth of the cold proton bunch stored at 250 GeV (no cooling) 57

58 Luminosity of gold-gold collisions 58

59 Cooling at RHIC The longitudinal bunch length vs. time for various cooling currents. The number of ions in a single bunch vs. time for various cooling currents. 59

60 Schematic layout of the cooling system next to a RHIC interaction point The electron cooling equipment comprises the following key elements: 1 A 2 MeV injector with a magnetized cathode (the magnetic field on the cathode of the injector is ~100 G). 3 A solenoid extension of the longitudinal magnetic field of the injector (100 G). 2,4 Skew quadrupoles for the transformation of the magnetized beam into a flat beam 6 Energy modulating cavity for reducing the electron bunch length from 4 ns to 0.06 ns. It consists of two 70 MHz RF-cavity (the gap voltage is 350 kv) and one 210 MHz (36 kv) RF-cavity. 5,7,8 Electron optical elements of the bunching system. 9,9' Magnetic compressor (an a-magnet, with a bending radius of 1m). 10,11,12,13 Electron optical elements of the bunching system. 14 RF linac structure (350 MHz LEP structure). 15 A bending magnet for a compensation of the action of the last high-energy (50 MeV) bending magnet (9''). 18 Third harmonic of the RF linac (1.05 GHz), for compensation of the non-linearity of fundamental accelerating field. 16,17,19,20,22,23 Electron optical elements of the debunching system. 21,21' Magnetic de-compressor (an a-magnet, with a bending radius of 1m). 24 RF-cavity for eliminating the linear energy chirp. It consists of 80 MHz RF cavity (the gap voltage is 4.6 MV) and 240 MHz (0.24 kv). This cavity should be superconducting. 25 Transfer optics from a flat to a round beam electron beam, for injection into the main solenoid. 26 Bending magnet. 27 Main solenoid (104 G). 28 Beam-dump or system of beam recuperation. 60

61 Schematic Drawing of the FEL Driven by an Accelerator-Recuperator good as prototype for ECooler at high energies! RF-Cavities Bending Magnets Quadrupoles Solenoids Undulators Bunchers Gun Dump 61

62 Schematic Drawing of the Submillimeter FEL and AR (the first step single turn) RF-Cavities Bending Magnets Quadrupoles Solenoids Undulators Buncher Mirrors Outcoupler 62

63 63 14 MeV accelerator-recuperator in operation.

64 ENC (GSI) Electron-Proton s max = 30 GeV L epmax = cm 2 s 1